Dwarf galaxies suggest dark matter theories may be wrong

In summary: Submitted on 17 Jul 2011)In summary, the article discusses the discrepancy between the kinematics of the bright satellites of the Milky Way and the predictions of simulations that assume the galaxies are made of cold dark matter. It is suggested that the discrepancy may be resolved if the galaxy is made of warm dark matter instead.
  • #1
phinds
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I realize BBC science news is not a totally reliable source, but I'm wondering if any of the knowledgeable folks here have any comment on this:

http://www.bbc.co.uk/news/science-environment-14948730

I tried to find if there had already been a thread on it, but I may have not looked hard enough. If there is one, just point me to it.
 
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  • #2
phinds said:
I realize BBC science news is not a totally reliable source, but I'm wondering if any of the knowledgeable folks here have any comment on this:

http://www.bbc.co.uk/news/science-environment-14948730

I tried to find if there had already been a thread on it, but I may have not looked hard enough. If there is one, just point me to it.
Well, the lack of dwarf galaxies is very well-known. However, the line connecting the lack of dwarf galaxies to dark matter isn't so easy, and for a rather simple reason: very small galaxies tend to expel most of their visible matter early-on, and so dwarf galaxies are really, really hard to detect. Most astrophysicists and cosmologists think it's more likely that we just aren't seeing the most of the dwarf galaxies. Warm dark matter is a possibility, but the evidence so far is sketchy at best.
 
  • #3
Dwarf galaxies are just another poorly accounted for contributor to baryonic mass in the universe. WMAP has already ruled out baryonic mass as a significant component of the 'missing' mass of the universe.
 
  • #4
Chronos said:
Dwarf galaxies are just another poorly accounted for contributor to baryonic mass in the universe. WMAP has already ruled out baryonic mass as a significant component of the 'missing' mass of the universe.

But the article is not arguing against dark matter at all, just arguing for warm dark matter rather than cold dark matter. Is there other evidence that suggests these guys are off on a wild goose chase? Chalnoth suggests that this is likely (the wild goose chase) but possibly could be onto something.

I take it that they MAY be onto something but more evidence is needed. Hm ... Chalnoth, I think I just restated what YOU said. :smile:
 
  • #5
I agree, they could be on to something and it seems worth checking out. Here is a related paper:

http://arxiv.org/abs/1104.2929
The Haloes of Bright Satellite Galaxies in a Warm Dark Matter Universe
Mark Lovell, Vincent Eke, Carlos Frenk, Liang Gao, Adrian Jenkins, Tom Theuns, Jie Wang, Alexey Boyarsky, Oleg Ruchayskiy
(Submitted on 14 Apr 2011)
High resolution N-body simulations of galactic cold dark matter haloes indicate that we should expect to find a few satellite galaxies around the Milky Way whose haloes have a maximum circular velocity in excess of 40 kms. Yet, with the exception of the Magellanic Clouds and the Sagittarius dwarf, which likely reside in subhaloes with significantly larger velocities than this, the bright satellites of the Milky Way all appear to reside in subhaloes with maximum circular velocities below 40 kms. As recently highlighted by Boylan-Kolchin et al., this discrepancy implies that the majority of the most massive subhaloes within a cold dark matter galactic halo are much too concentrated to be consistent with the kinematic data for the bright Milky Way satellites. Here we show that no such discrepancy exists if haloes are made of warm, rather than cold dark matter because these haloes are less concentrated on account of their typically later formation epochs. Warm dark matter is one of several possible explanations for the observed kinematics of the satellites.
6 pages, 5 figures

The paper by Lovell et al refers to this one submitted in late February, to be published in MNRAS letters:

http://arxiv.org/abs/1103.0007
Too big to fail? The puzzling darkness of massive Milky Way subhaloes
Michael Boylan-Kolchin, James S. Bullock, Manoj Kaplinghat
(Submitted on 28 Feb 2011)
We show that dissipationless LCDM simulations predict that the majority of the most massive subhaloes of the Milky Way are too dense to host any of its bright satellites (LV > 105 Lsun). These dark subhaloes have circular velocities at infall of 30-70 km/s and infall masses of [0.2-4] x 1010 Msun. Unless the Milky Way is a statistical anomaly, this implies that galaxy formation becomes effectively stochastic at these masses. This is in marked contrast to the well-established monotonic relation between galaxy luminosity and halo circular velocity (or halo mass) for more massive haloes. We show that at least two (and typically four) of these massive dark subhaloes are expected to produce a larger dark matter annihilation flux than Draco. It may be possible to circumvent these conclusions if baryonic feedback in dwarf satellites or different dark matter physics can reduce the central densities of massive subhaloes by order unity on a scale of 0.3 - 1 kpc.
6 pages, 5 figures

I see that Simon White of the Garching Max Planck Institute for Astrophysics is in on this paper as a co-author with Carlos Frenk:
http://arxiv.org/abs/1107.1916
Where will supersymmetric dark matter first be seen?
L. Gao, C. S. Frenk, A. Jenkins, V. Springel, S. D. M. White
(Submitted on 11 Jul 2011)
I believe this was already published in MNRAS. The material is somewhat related to what was discussed in the other two.

Another related paper (quite a lot of activity on this idea recently)
http://arxiv.org/abs/1105.3474
The Baryons in the Milky Way Satellites
Owen H. Parry, Vincent R. Eke, Carlos S. Frenk, Takashi Okamoto
(Submitted on 17 May 2011 (v1), last revised 22 Jun 2011 (this version, v2))
We investigate the formation and evolution of satellite galaxies using smoothed particle hydrodynamics (SPH) simulations of a Milky Way(MW)-like system, focussing on the best resolved examples, analogous to the classical MW satellites. Comparing with a pure dark...
...or the subhalos may have initially formed with lower concentrations as would be the case, for example, if the dark matter were made of warm, rather than cold particles.
16 pages, 11 figures
 
Last edited:
  • #6
Very cool ... thank you Marcus
 

1. What is a dwarf galaxy?

Dwarf galaxies are small, low-mass galaxies that typically contain a few billion stars. They are considered to be the building blocks of larger galaxies and are the most numerous type of galaxy in the universe.

2. How do dwarf galaxies suggest that dark matter theories may be wrong?

Dwarf galaxies have lower levels of dark matter compared to other types of galaxies, which challenges the current theories of dark matter. This suggests that there may be alternative explanations for the observed gravitational effects that are typically attributed to dark matter.

3. What is dark matter?

Dark matter is a hypothetical type of matter that does not emit or absorb light, making it invisible to telescopes. It is thought to make up about 85% of the total matter in the universe and is believed to play a major role in the formation and evolution of galaxies.

4. How do scientists study dwarf galaxies?

Scientists use a variety of methods to study dwarf galaxies, including observations from telescopes, computer simulations, and analyzing the motions of stars within the galaxy. They also study the chemical composition and structure of these galaxies to understand their evolution.

5. What are some alternative theories to explain the observed effects of dark matter?

Some alternative theories propose modifications to the laws of gravity, such as modified Newtonian dynamics (MOND), which could explain the observed effects without the need for dark matter. Other theories suggest that dark matter may be composed of particles that interact differently with gravity, such as axions or weakly interacting massive particles (WIMPs).

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